Tight bifunctional hierarchical catalyst

Karen T. Højholt, Peter N. R. Vennestrøm, Ramchandra Tiruvalam, Pablo Beato
2011 Chemical Communications  
All reagents were of reagent grade and used without any further purification: Sodium molybdate dihydrate (Na 2 MoO 4 ·2H 2 O, ≥99.5 wt%, Sigma-Aldrich), nitric acid (HNO 3 , 65 wt%, Sigma-Aldrich), cobalt(II) sulfate heptahydrate (CoSO 4 ·7H 2 O, 99 wt%, Sigma-Aldrich), sodium peroxodisulfate (Na 2 S 2 O 8 , ≥99 wt%, Aldrich), sodium hydroxide (NaOH, 99 wt%, Riedel-de Häen), ammonium nitrate (NH 4 NO 3 , 99.5 wt%, Merck), ammonia (NH 3 , 25 wt%, Fluka), toluene (C 7 H 8 , 99.7 wt%, Fluka),
more » ... inopropyl)trimethoxysilane (APTMS, 97 wt%, Aldrich), hydrochloric acid (HCl, 37 wt%, Sigma-Aldrich). Synthesis of Na 3 [Co(OH) 6 Mo 6 O 18 ] ·8H 2 O Na 3 [Co(OH) 6 Mo 6 O 18 ] was synthesised according to Nolan et al. 1 using the following procedure: First, 30.26 g Na 2 MoO 4 ·2H 2 O was dissolved in 50 ml H 2 O and acidified to pH 4.51 with HNO 3 (65 wt%). In another beaker 5.75 g CoSO 4 ·7 H 2 O was dissolved in 10 ml H 2 O and then added to the molybdate solution under stirring. A solution of 7.53 g Na 2 S 2 O 8 dissolved in 8.8 ml H 2 O was then added to the Co/Mo mixture as an oxidising agent. The obtained solution was heated to reflux until a dark turquoise solid precipitated. Upon further refluxing, the precipitate was redissolved and the original red colour of the solution returned. Following this, the solution gradually turned dark green, a color change indicating oxidation of the cobalt (II) to cobalt (III). Boiling was continued until evolution of oxygen ceased, by which time the solution became permanently dark turquoise. Finally the hot solution was filtered and the filtrate was left to precipitate dark green crystals upon cooling and consecutive evaporation of the solvent. The product is referred to as CoMo 6 . Synthesis of mesoporous ZSM-5 Hierarchical ZSM-5 was prepared by desilication of a commercially available ZSM-5 zeolite using a 0.3 M NaOH solution (33 ml per gram zeolite) for 30 min at 70 ºC. The selective silicon leaching was stopped by quenching the solution in an ice-bath, and then washed three times with water by centrifugation. The desilicated ZSM-5 was dried over night at room temperature before further treatment. To obtain the ammonium form of the desilicated samples two consecutive ion exchanges were carried out using a 1.7 M NH 4 NO 3 /0.94 M NH 3 buffer solution with 10 ml solution per gram zeolite, at 80 ºC under stirring for 2 hours. After each exchange, the NH 4 -form of the zeolite was isolated by filtration, washed with water and dried in air at 110 ºC. After the last ion exchange, the H-form of the desilicated zeolite was finally obtained by calcining the NH 4 -form in air to 550ºC for 3 h. Anchoring CoMo 6 on mesoporous ZSM-5 The CoMo 6 clusters were anchored onto the mesopore surface of hierarchical ZSM-5 by first functionalising the surface with (3-aminopropyl)trimethoxysilane (APTMS): 4 g of mesoporous ZSM-5 were suspended in 160 ml toluene and heated to 65 ºC, followed by the addition of 11 g APTMS. The suspension was stirred overnight, filtered and the obtained product washed with toluene and dried at room temperature. 2 g of functionalised mesoporous ZSM-5 were stirred over night in 150 ml 3 M HCl, filtered and left for drying at room temperature. The CoMo 6 Anderson ion Electronic Supplementary Material (ESI) for Chemical Communications This journal is
doi:10.1039/c1cc15413c pmid:22048337 fatcat:xxlxmrd3q5a2dppfdmll6itcva